1. Related Field
The invention relates to three-dimensional imaging of physical objects. In particular, the invention relates to laser imaging of dental items including molds, castings, dentition, prepared dentition and the like.
2. Description of the Related Art
Techniques have been developed to generate three-dimensional (“3D”) visual images of physical objects. The 3D image may be generated by a computer that processes data representing the surfaces and contours of a physical object. The computer displays the 3D image on a screen or a computer monitor. The data may be generated by optically scanning the physical object and detecting or capturing the light reflected off of the object. Based on processing techniques such as Moiré, interferometry, and laser triangulation the shape, surfaces and/or contours of the object may be modeled by the computer.
The Moiré technique uses a structured white light to project a 2D image on the object to be imaged. The Moiré technique uses a pattern that has a sinusoidal intensity pattern. The projected image intensity pattern observed from a position other than the projected angle does not appear sinusoidal. Therefore, an inferred point-by-point phase angle between an observed and a projected image may be correlated to the height data Z at each observed pixel point. Interferometry methods may then use a reference beam and a scanning beam to infer 3D information based on an optical interference between the two beams.
Laser triangulation methods project a laser dot or beam onto an object from a known direction. The laser beam is scanned across the surface of the object following an arc. The laser beam is imaged by an imaging system from a different known direction. The known baseline and angle between the projector and imaging system provides sufficient information to deduce the 3D location of the reflected dot from the surface of the object being scanned, utilizing known triangulation techniques. Such scanning may also result in an inaccurate reading of depth of field and uniformity of a line width due to the scanned arc. Systems have been developed using special optics that increase the depth measurement and resolution. However, some special optics adversely effect and distort the optical image and limit the speed at which the system may acquire sufficient data to generate a 3D image.
Laser triangulation methods also may scan one or more laser lines across an object. The laser lines may be generated through a diffractive lens. However, the intensity of the laser line(s) may vary along the length of the projected line(s), resulting in inaccurate measurements and imaging of the object. The laser line systems are also susceptible to laser speckle, which may appear as a mottled pattern of randomly distributed “blobs of light.” Laser speckle may be caused by an interference at the image plane of coherent light reflected by a rough surface. The mottled pattern may introduce noise and uncertainty into the measurement, due to a difficulty in distinguishing between useful intensity data, and speckle intensity data.
Current laser systems used in dental applications may be rudimentary and limited by the projection of a single laser line. Such systems are not adjustable for a desired line pattern and lack any correction or minimization of a non-flat or non-linear scanning field or correction for laser speckle. Also, such systems may have a limited clamping and holding mechanism which limit the range of molds or castings for which the digitizer may be used.